XRTypeRS

Hiya,

Now I have my techedge AFR meter fully installed I have found that at idle / cruise off boost I have an AFR of about 12.5 which seems too low and I guess might mean my car will fail the MOT. Therefore Id like to build myself a 5th injector setup so I can dial back the EMFPR on the KE Jet and get a better AFR off boost but still have enough fuel on boost to maintain the 11.2 AFR Im getting now.

I have been knocking a few circuit ideas round in my head of how I might drive the injector. Basically I will want it to kick in at a preset boost level so I could achive this with either a MAP sensor (Motorola MPX4250) or a simple pressure switch. Then I'll need something to drive the injector and to be able to vary the duty cycle to hense vary fuelling. To to this I was planning to use a simple 555 timer based monostable circuit which could be driven by :-

a). Another 555 in astable mode so when the boost level got to the "on" pressure a set additional amount of fuel would be provided regardless of RPM.

or

b). I could use the dizzy signal to trigger the monostable so once the injector kicks in the extra fuelling will increase linearly with RPM.

I realise that the engines fuel requirements are not linear but given Im ony looking to run 14 psi max would one of these crude systems be sufficient??.

Alternatively I considered using an LM2907 frequency to voltage convertor IC to give me a way of measuring RPM and allowing me to vary the duty cycle of the drive to the injector with RPM so give a bit more refinement.

Anyone got any views?? - I know its not going to be anywhere as good as an MF2 etc but it might be good enough for my needs??

Cheers

Stu

Jim Galbally

do a google search for "megasquirt"

you can build it for pennies and it will do everything you need..

why design the wheel when the wheel's already been designed?

XRTypeRS

Jim I've looked at Megasquirt and it looks very good however its more complex than I really need to go at the moment and cheap tho it is for what it is I want to make something a lot cheaper if I can, i.e. <Ł50 - Im sure it must be possible

Jim Galbally

have you looked at MSD's 5th injector drivers? theyre cheap n work well...

basically what youre doing may only be marginally cheaper than buying a product off the shelf, and will be a hell of a lot worse than said product...

or get someone ho actually knows about KE-JET to set up your metering head PROPERLY so it passes MOTs and fuels fine on boost.

i know DIY is fun, but most of the time it is CHEAPER justto pay an expert to sort it...

XRTypeRS

I see your point mate but doing this sort of thing is why I like having an RS and to be honest the only person I trust to do anything on my car these days is me

Jim Galbally

ok well in that case what you're thinking of will work...

ive seen MUCh more crude methods used...

the thing is if the slightest little thng went wrong (car bosts a bit too much, too little, a wire snaps, bla blah blah you can kill your engine...

it would need more safety features IMHO...

ke CAN do what you want it to do tho mate, so my advice is to read up on that and see how it works... ic an email you the K-JET manual, but this is missing all the bits that KE has like EMFPRs and stuff...

a god starting ground tho... willdo it when i get to work tomorrow.